Commonly assigned U.S. patent application Ser. No. 12/421,325 describes apparatus and methods for recovering hydrocarbonaceous and additional products from nonrubilized oil shale and oil/tar sands. The method comprises the steps of forming a hole in a body of nonrubilized oil shale or sand, positioning a gas inlet conduit into the hole, and introducing a heated, pressurized processing gas into the hole through the inlet, thereby creating a nonburning thermal energy front sufficient to convert kerogen in oil shale or bitumen in oil sand to hydrocarbonaceous products. The processing gas and hydrocarbonaceous products are withdrawn as effluent gas through the hole, and a series of condensation steps are performed on the effluent gas to recover various products.
In the preferred embodiment, a negative pressure relative to the well inlet pressure is maintained to ensure positive flow of the combustion and product gases, this is performed by a method of blowers on the front and or back side of the well and the removal of mass during the condensation steps. Also in the preferred embodiment, one or more initial condensation steps are performed to recover crude-oil products from the effluent gas, followed by one or more subsequent condensation steps to recover additional, non-crude-oil products from the effluent gas. In conjunction with oil/tar sands, the method includes the step of providing an apertured sleeve within the hole to limit excessive in-fill.
In accordance with the above-referenced application, a basic system for recovering hydrocarbonaceous and other products from a hole drilled in nonrubilized oil shale and oil/tar sands comprises a combustor for heating and pressurizing a processing gas, a gas inlet conduit for introducing the processing gas into the hole to convert kerogen in oil shale or bitumen in oil sand into hydrocarbonaceous products, and a gas outlet conduit for withdrawing the processing gas and hydrocarbonaceous products from the hole. Through the use of multiple condensation steps to recover non-crude products, negative down-well pressure to fine-tune extraction parameters, and carbon sequestration techniques, the disclosed apparatus and methods are significantly more ‘environmentally friendly’ when compared to previous approaches.
Nevertheless, environmental issues remain. In particular, groundwater vulnerability, hazards, and protection will always be major concerns relating to current surface retorting or other in situ recovery oil shale operations. Much of Colorado, Wyoming and Utah—where large oil shale and sands deposits are present—have very limited water resources. Groundwater is the major source for drinking, irrigation and other uses. Present water consumption exceeds natural replenishment. Recently water pollution problems have placed an additional strain on scarce water resources.
Other in situ processes offer a very attractive proposition because of they reduce standard surface environmental problems, but some of these processes involve potentially significant environmental costs to aquifers. These methods can cause groundwater contamination because the hydraulic conductivity of the remaining spent shale increases and allows groundwater to flow through and leach salts, arsenic, selenium, other metals and volatile and aromatic organic contaminates into the aquifer. Some companies are enhancing groundwater contamination potential by performing massive subsurface rubilization efforts and or using high pressure induction processes which cannot be controlled and ultimately lead to groundwater contamination potential. Processing of oil shale and sands has over seventy years of serious application mostly ex situ—surface retorting, not many companies that develop these or similar resources have successfully deployed technologies to protect groundwater.
Shell, a major participant in oil shale development, attempts to solve the problem by erecting an “ice wall” around their production wells. The ice wall is a 30-feet-thick frozen barrier that extends from the surface to 1,700 feet below the ground and prevents both groundwater from seeping in and chemicals and contaminants from seeping out. The wall is pumped full of an ammonia-based coolant and takes about eighteen (18) months for the adjacent water and rock to freeze to −60° F. to create the massive ice wall. This method is very expensive to maintain and involves very large power inputs and doesn't address the potential post barrier contamination problems and has had failure problems which can result in no effective protection. Other companies are trying avoidance. For example, American Shale Oil is targeting specific layers of oil shale in order to avoid contact with groundwater. This approach limits the application of their technology to only a few locations.